Tekashi69 was just turned away at the door trying to attend fight night on Long Island, and our sources say it’s connected to a shooting months ago at the Barclays Center.

The rapper was stopped by security at the Nassau Coliseum in NY Saturday night as he was trying to make his way in for “Bellator 208: Fedor vs. Sonnen” … sources close to the situation tell TMZ Sports.

We’re told 6ix9ine planned to meet up with his pal and Bellator brand ambassador 50 Cent, but wasn’t allowed entry. Fiddy wasn’t there yet anyway … but we’re told it wouldn’t have mattered.

As for why Tekashi’s barred … our sources say it stems from a shooting back in April at the Barclays Center connected to Tekashi’s manager, Tr3yway. The same company that owns the Nassau Coliseum owns Barclays, and as we reported … the rapper’s persona non grata at that venue.

So … we’re told it’s a case of the rapper being 86’d at both arenas. We also reached out to Bellator … they had no comment.

Sources close to Tekashi have responded to the incident, telling us … “It is unfortunate a venue would take it upon itself to treat a person unfairly based on allegations. What happened tonight at the Nassau Coliseum is disappointing.”